The invention relates to methods and arrangements for gasifying finely divided solid combustible material.
Gasifiers are already known for gasifying finely divided solid combustible material by mixing the same with a combustion-supporting gas such as air, oxygen-enriched air or pure oxygen. The combustible material is reacted with the combustion-supporting gas, sometimes with the addition of steam, so that the combustible material becomes partially combusted, producing a gas mixture containing carbon monoxide and hydrogen. The gasifying process can be successfully performed at very low pressures, for example only slightly above atmospheric pressure, and also at high pressures, such as between about 2 and 80 atm.
Persons familar with gasification techniques are well aware that finely divided solid combustible material, such as coal dust, is highly reactive and will explode with great force if oxygen is present. The explosion can be triggered by the smallest spark. For this reason it is necessary to keep the combustible material removed from combustion-supporting gas until the combustible material enters the gasifier. This can be accomplished by maintaining the combustible material in an environment of inert gas, such as nitrogen or other gas incapable of supporting combustion. If the finely divided solid combustible material is fluidized, for ease of handling, then the fluidizing gas employed will be the inert gas just mentioned. If inert fluidizing gas is employed in this manner it becomes possible to prevent the combustible material from becoming mixed with combustion-supporting gas until the combustible material is actually delivered to the gasifier, or mixed with combustion-supporting gas in some other controlled manner.
Despite the use of an inert gas for fluidizing finely divided solid combustibles, the possibility of such combustibles becoming mixed with combustion-supporting gas still exists. Specifically, a conduit necessarily leads from the source of fluidized combustible material to an inlet of the gasifier, and another conduit leads from the source of combustion-supporting gas to the gasifier. It is possible, therefore, for combustion-supporting gas to enter the conduit leading from the source of combustible material and become mixed with combustibles before the combustibles have entered the gasifier. As explained above, this is exceedingly dangerous.